1. Field of the Invention
The present invention relates to sterilization of articles. More particularly, the present invention relates to sterilization by irradiation and radiolyric decomposition of substrates and consequent release of a sterilant gas.
2. Description of Related Art
Sterilization and disinfection are important procedures used for the reduction or elimination of disease causing organisms or agents. Sterilization and disinfection are very important, e.g., in sanitation or medicine to reduce or prevent the spread of infections and the like.
Traditional methods of sterilization include the use of steam, dry heat, chemicals, and radiation. Steam and dry heat, while effective in certain cases, require high temperatures which may not be suitable for all products which are to be used or reused. Chemicals which are used for sterilization include gases such as ethylene oxide, propylene oxide, formaldehyde, glutaraldehyde, methyl bromide, ozone and propriolactone. Chemical sterilants are useful on materials which may be sensitive to the effects of heat or moisture.
A popular gas sterilant is ethylene oxide which, unfortunately, is potentially explosive and is primarily a surface sterilant. Formaldehyde has also been used but drawbacks include instability of stock solutions, toxicity, the need for heat and humidity in certain instances, explosiveness at typical gas phase concentrations, and a substantial lack of penetration into the object being sterilized.
Radiation sterilization includes the use of ultraviolet rays, electron beams, x-rays, gamma rays, and to a limited extent, gas plasma and microwave radiation. Some radiation sterilization is considered to be a volume sterilant, i.e., capable of good penetration and sterilizing throughout a volume with substantially equal results. However, ultraviolet radiation and gas plasma are predominantly surface sterilants without substantial penetration. Moreover, most forms of radiation are known to degrade certain polymers and may be detrimental to products incorporating those polymers.
Attempts have been made to combine certain of the above sterilants. For example, U.S. Pat. No. 3,117,832 describes simultaneous use of toxic gases such as ethylene oxide or propylene oxide, ozone and ultraviolet rays. Swiss Patent No. 387,881 describes sterilization by the simultaneous action of vapors of methanogen, trioxymethylene, formaldehyde, or aldylene, with ozone and ultraviolet rays. The vapors are released into the chamber by heating. Japanese Kokai 55-116354 describes artificial kidney sterilization with an aqueous solution of formaldehyde in combination with gamma irradiation and avoidance of gas bubbles.
Generation of a gas sterilant or disinfectant has been an important field of study. For example, a chlorine dioxide gas disinfectant may be generated by subjecting a solid chlorite to ultraviolet radiation as is described in U.S. Pat. No. 4,874,489. Sustained release of a gaseous sterilant is described in U.S. Pat. No. 4,717,544 where solid polymeric aldehydes are thermally depolymerized to afford gas phase monomers. U.S. Pat. Nos. 4,400,357, 5,019,344 and 5,019,359 describe generation of gas sterilants by heating with microwave radiation. The '344 and '359 patents involve the combined effect of microwave radiation and the gas sterilant on the object to be sterilized. Packages containing an object to be sterilized and a sterilant which is heat releasably bonded to a substrate are described in U.S. Pat. No. 3,494,726. U.S. Pat. No. 4,050,576 describes subjecting a polyacetal to high energy irradiation without effecting depolymerization, which as a result, can then be depolymerized by heating. The preirradiated polyacetal is placed in a sterilant package.
All the above described methods of generating a gaseous sterilant or disinfectant, with the exception of the '489 patent, involve generation of the sterilant gas by means of heat. As was noted above, heat is not suitable for all sterilization applications. Consequently, there is a need for novel sterilization systems and techniques which reduce or eliminate the disadvantages described above.